Historic Mecca, the cradle of Islam, is being buried in an unprecedented onslaught by religious zealots.

Almost all of the rich and multi-layered history of the holy city is gone. The Washington-based Gulf Institute estimates that 95 per cent of millennium-old buildings have been demolished in the past two decades.

Now the actual birthplace of the Prophet Mohamed is facing the bulldozers, with the connivance of Saudi religious authorities whose hardline interpretation of Islam is compelling them to wipe out their own heritage.

It is the same oil-rich orthodoxy that pumped money into the Taliban as they prepared to detonate the Bamiyan buddhas in 2000. And the same doctrine - violently opposed to all forms of idolatry - that this week decreed that the Saudis' own king be buried in an unmarked desert grave.

A Saudi architect, Sami Angawi, who is an acknowledged specialist on the region's Islamic architecture, told The Independent that the final farewell to Mecca is imminent: "What we are witnessing are the last days of Mecca and Medina."

According to Dr Angawi - who has dedicated his life to preserving Islam's two holiest cities - as few as 20 structures are left that date back to the lifetime of the Prophet 1,400 years ago and those that remain could be bulldozed at any time. "This is the end of history in Mecca and Medina and the end of their future," said Dr Angawi.

Mecca is the most visited pilgrimage site in the world. It is home to the Grand Mosque and, along with the nearby city of Medina which houses the Prophet's tomb, receives four million people annually as they undertake the Islamic duty of the Haj and Umra pilgrimages.

The driving force behind the demolition campaign that has transformed these cities is Wahhabism. This, the austere state faith of Saudi Arabia, was imported by the al-Saud tribal chieftains when they conquered the region in the 1920s.

The motive behind the destruction is the Wahhabists' fanatical fear that places of historical and religious interest could give rise to idolatry or polytheism, the worship of multiple and potentially equal gods.

The practice of idolatry in Saudi Arabia remains, in principle at least, punishable by beheading. This same literalism mandates that advertising posters can and need to be altered. The walls of Jeddah are adorned with ads featuring people deliberately missing an eye or with a foot painted over. These contrived imperfections are the most glaring sign of an orthodoxy that tolerates nothing which fosters adulation of the graven image. Nothing can, or can be seen to, interfere with a person's devotion to Allah.

"At the root of the problem is Wahhabism," says Dr Angawi. "They have a big complex about idolatry and anything that relates to the Prophet."

The Wahhabists now have the birthplace of the Prophet in their sights. The site survived redevelopment early in the reign of King Abdul al-Aziz ibn Saud 50 years ago when the architect for a library there persuaded the absolute ruler to allow him to keep the remains under the new structure. That concession is under threat after Saudi authorities approved plans to "update" the library with a new structure that would concrete over the existing foundations and their priceless remains.

Dr Angawi is the descendant of a respected merchant family in Jeddah and a leading figure in the Hijaz - a swath of the kingdom that includes the holy cities and runs from the mountains bordering Yemen in the south to the northern shores of the Red Sea and the frontier with Jordan. He established the Haj Research Centre two decades ago to preserve the rich history of Mecca and Medina. Yet it has largely been a doomed effort. He says that the bulldozers could come "at any time" and the Prophet's birthplace would be gone in a single night.

He is not alone in his concerns. The Gulf Institute, an independent news-gathering group, has publicised what it says is a fatwa, issued by the senior Saudi council of religious scholars in 1994, stating that preserving historical sites "could lead to polytheism and idolatry".

Ali al-Ahmed, the head of the organisation, formerly known as the Saudi Institute, said: "The destruction of Islamic landmarks in Hijaz is the largest in history, and worse than the desecration of the Koran."

Most of the buildings have suffered the same fate as the house of Ali-Oraid, the grandson of the Prophet, which was identified and excavated by Dr Angawi. After its discovery, King Fahd ordered that it be bulldozed before it could become a pilgrimage site.

"The bulldozer is there and they take only two hours to destroy everything. It has no sensitivity to history. It digs down to the bedrock and then the concrete is poured in," he said.

Similarly, finds by a Lebanese professor, Kamal Salibi, which indicated that once-Jewish villages in what is now Saudi Arabia might have been the location of scenes from the Bible, prompted the bulldozers to be sent in. All traces were destroyed.

This depressing pattern of excavation and demolition has led Dr Angawi and his colleagues to keep secret a number of locations in the holy cities that could date back as far as the time of Abraham.

The ruling House of Saud has been bound to Wahhabism since the religious reformer Mohamed Ibn abdul-Wahab signed a pact with Mohammed bin Saud in 1744. The combination of the al-Saud clan and Wahhab's warrior zealots became the foundation of the modern state. The House of Saud received its wealth and power and the hardline clerics got the state backing that would enable them in the decades to come to promote their Wahhabist ideology across the globe.

On the tailcoats of the religious zealots have come commercial developers keen to fill the historic void left by demolitions with lucrative high-rises.

"The man-made history of Mecca has gone and now the Mecca that God made is going as well." Says Dr Angawi. "The projects that are coming up are going to finish them historically, architecturally and environmentally," he said.

With the annual pilgrimage expected to increase five-fold to 20 million in the coming years as Saudi authorities relax entry controls, estate agencies are seeing a chance to cash in on huge demand for accommodation.

"The infrastructure at the moment cannot cope. New hotels, apartments and services are badly needed," the director of a leading Saudi estate agency told Reuters.

Despite an estimated $13bn in development cash currently washing around Mecca, Saudi sceptics dismiss the developers' argument. "The service of pilgrims is not the goal really," says Mr Ahmed. "If they were concerned for the pilgrims, they would have built a railroad between Mecca and Jeddah, and Mecca and Medina. They are removing any historical landmark that is not Saudi-Wahhabi, and using the prime location to make money," he says.

Dominating these new developments is the Jabal Omar scheme which will feature two 50-storey hotel towers and seven 35-storey apartment blocks - all within a stone's throw of the Grand Mosque.

Dr Angawi said: "Mecca should be the reflection of the multicultural Muslim world, not a concrete parking lot."

Whereas proposals for high-rise developments in Jerusalem have prompted a worldwide outcry and the Taliban's demolition of the Bamiyan buddhas was condemned by Unicef, Mecca's busy bulldozers have barely raised a whisper of protest.

"The house where the Prophet received the word of God is gone and nobody cares," says Dr Angawi. "I don't want trouble. I just want this to stop."